1. Field of the Invention
Olefin metathesis (disproportionation) in its simplest form describes the reversible, metal-catalyzed rearrangement of olefins by cleavage and reformation of C.dbd.C double bonds. For example, olefins of the formulae R.sup.1 --CH.dbd.CH--R.sup.2 and R.sup.3 --CH.dbd.CH--R.sup.4 are reversibly reacted to form olefins of the formulae R.sup.1 --CH.dbd.CH--R.sup.3 and R.sup.2 --CH.dbd.CH--R.sup.4. In the metathesis of acyclic olefins, a distinction is made between self-metathesis in which an olefin is converted into a mixture of two olefins having different molar masses and cross- or co-metathesis in which two different olefins react. An example of self-metathesis is the reaction of two molecules of propene to give ethene and 2-butene, as is performed, for example, by the Phillips triolefin process, see Hydrocarbon Processing, Volume 46, November 1967, No. 11, p. 232. An example of cross-metathesis is the reaction of propene and 1-butene to give ethene and 2-pentene. If one of the reactants is ethene, the reaction is customarily referred to as an ethenolysis.
The metathesis reactions are carried out in the presence of catalysts. Suitable catalysts for this purpose are, in principle, homogeneous and heterogeneous transition metal compounds, in particular those of transition groups VI to VIII of the Periodic Table of the Elements, as well as homogeneous and heterogeneous catalyst systems in which these compounds are present.
2. Description of the Prior Art
DE-A-19 40 433 discloses the metathesis of 1-butene with 2-butene to form propene and 2-pentene, with Re.sub.2 O.sub.7 /Al.sub.2 O.sub.3 being used as catalyst. The 2-pentene formed is reacted further with sodium hydride on potassium carbonate and ethene to give heptenes.
The metathesis of 1-butene and 2-butene to give propene and 2-pentene is mentioned in K. L. Anderson, T. D. Brown, Hydrocarbon Processing, Volume 55, August 1978, No. 8, pp. 119-122 as a secondary reaction in the synthesis of isoamylene.
EP-A-0 304 515 discloses a metathesis process for reacting 1-butene with 2-butene to give propene and pentenes, which is carried out in a reactive distillation apparatus using Re.sub.2 O.sub.7 /Al.sub.2 O.sub.3 as catalyst.
U.S. Pat. No. 3,526,676 discloses the metathesis of 1-butene with 2-butene to give propene and pentene. It is carried out over MoO.sub.3 and CoO on Al.sub.2 O.sub.3.
U.S. Pat. No. 3,785,957 discloses a process for the production of fuel having a high octane number. In this process, an olefinic fuel is disproportionated together with ethylene, the product is fractionated into a propylene stream, a butene stream, a C.sub.5 - or C.sub.5 -C.sub.6 -olefin stream and a C.sub.6+ or C.sub.7+ fuel stream. The C.sub.5 - or C.sub.5 -C.sub.6 -olefin stream is disproportionated with ethene over a WO.sub.3 /SiO.sub.2 fixed-bed catalyst to give propylene and butenes. The propylene obtained is disproportionated to form ethylene and butenes and the butenes are alkylated with isobutane.
U.S. Pat. No. 3,767,565 discloses a process for increasing the octane number of fuel in which a C.sub.5 fraction of an olefinic fuel is reacted with ethylene in the presence of a catalyst comprising WO.sub.3 /SiO.sub.2 and MgO to form ethylene, propylene, n-butenes and isobutenes. The propylene obtained is disproportionated and the resulting n-butenes are alkylated with isobutane.
EP-A1-0 691 318 discloses an olefin metathesis process in which C.sub.5 -olefins and ethylene are reacted in the presence of a catalyst to give mixed C.sub.4 -olefins and propene. Thus, 2-methyl-2-butene is reacted with ethene to give isobutene and propene. A mixture of 2-pentenes and 2-methyl-2-butene is reacted to give a mixture of 1-butene, isobutene and propene.
A process for preparing propene in high yield by reacting 1-butene and 2-butene is not known.
A process for preparing propene in high yield by from 2-butene without use of a large excess of ethene is not known.